U.S. patent application number 15/244200 was filed with the patent office on 2016-12-08 for shovel and method of controlling shovel.
The applicant listed for this patent is SUMITOMO(S.H.I.) CONSTRUCTION MACHINERY CO., LTD.. Invention is credited to Tetsuya SUGAYA.
Application Number | 20160356021 15/244200 |
Document ID | / |
Family ID | 53878188 |
Filed Date | 2016-12-08 |
United States Patent
Application |
20160356021 |
Kind Code |
A1 |
SUGAYA; Tetsuya |
December 8, 2016 |
SHOVEL AND METHOD OF CONTROLLING SHOVEL
Abstract
A shovel includes a lower traveling body, an upper rotating body
mounted on the lower traveling body, an internal-combustion engine
including a supercharger and being controlled at a constant
revolution speed, a hydraulic pump coupled to the
internal-combustion engine, a hydraulic actuator to be driven by a
hydraulic oil discharged from the hydraulic pump, a control valve
system including multiple flow control valves for controlling a
flow of the hydraulic oil discharged from the hydraulic pump, and a
controller that controls an absorbing horsepower of the hydraulic
pump. The controller is configured to increase a boost pressure of
the supercharger before a load is applied to the hydraulic actuator
by controlling a specific flow control valve in the control valve
system to limit or block the flow of the hydraulic oil discharged
from the hydraulic pump and thereby increasing a discharge pressure
of the hydraulic pump.
Inventors: |
SUGAYA; Tetsuya; (Chiba,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO(S.H.I.) CONSTRUCTION MACHINERY CO., LTD. |
Tokyo |
|
JP |
|
|
Family ID: |
53878188 |
Appl. No.: |
15/244200 |
Filed: |
August 23, 2016 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2015/053771 |
Feb 12, 2015 |
|
|
|
15244200 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
E02F 9/2235 20130101;
F15B 2211/20546 20130101; E02F 9/2292 20130101; F02D 29/04
20130101; Y02T 10/12 20130101; F15B 2211/851 20130101; E02F 3/32
20130101; F15B 21/001 20130101; F15B 2211/6651 20130101; Y02T
10/144 20130101; E02F 9/2228 20130101; E02F 9/2285 20130101; E02F
9/2232 20130101; E02F 9/2246 20130101; F15B 2211/20523 20130101;
F02D 23/00 20130101; E02F 9/2282 20130101; E02F 9/2296
20130101 |
International
Class: |
E02F 9/22 20060101
E02F009/22; F02D 29/04 20060101 F02D029/04; F15B 21/00 20060101
F15B021/00; F02D 23/00 20060101 F02D023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 24, 2014 |
JP |
2014-033316 |
Claims
1. A shovel comprising: a lower traveling body; an upper rotating
body mounted on the lower traveling body; an internal-combustion
engine mounted on the upper rotating body and including a
supercharger, the internal-combustion engine being configured to be
controlled at a constant revolution speed; a hydraulic pump coupled
to the internal-combustion engine; a hydraulic actuator to be
driven by a hydraulic oil discharged from the hydraulic pump; a
control valve system including a plurality of flow control valves
for controlling a flow of the hydraulic oil discharged from the
hydraulic pump; and a controller that controls an absorbing
horsepower of the hydraulic pump, wherein the controller is
configured to increase a boost pressure of the supercharger before
a load is applied to the hydraulic actuator by controlling a
specific flow control valve in the control valve system to limit or
block the flow of the hydraulic oil discharged from the hydraulic
pump and thereby increasing a discharge pressure of the hydraulic
pump.
2. The shovel as claimed in claim 1, further comprising: an end
attachment, wherein the controller is configured to increase the
absorbing horsepower of the hydraulic pump regardless of whether a
reaction force received by the end attachment from a work object
increases or decreases.
3. The shovel as claimed in claim 1, wherein the controller is
configured to fine-tune the boost pressure of the supercharger by
increasing or decreasing a discharge rate of the hydraulic
pump.
4. The shovel as claimed in claim 1, wherein the controller is
configured to increase the boost pressure of the supercharger
before the load is applied to the hydraulic actuator by increasing
the discharge pressure of the hydraulic pump in a standby mode.
5. The shovel as claimed in claim 1, wherein the controller
includes a switcher configured to activate and deactivate a
function to increase the discharge pressure of the hydraulic
pump.
6. The shovel as claimed in claim 1, wherein the specific flow
control valve is disposed downstream of one of the flow control
valves that is related to the hydraulic actuator.
7. The shovel as claimed in claim 1, wherein the specific flow
control valve is disposed between the hydraulic pump and one of the
flow control valves that is related to the hydraulic actuator.
8. The shovel as claimed in claim 1, wherein the specific flow
control valve is a spool valve that operates only when a raising
operation of a boom is performed and does not operate when a
lowering operation of the boom is performed.
9. The shovel as claimed in claim 1, wherein the controller is
configured to control the boost pressure of the supercharger
according to an atmospheric pressure before the load is applied to
the hydraulic actuator.
10. A method for controlling a shovel including a lower traveling
body, an upper rotating body mounted on the lower traveling body,
an internal-combustion engine mounted on the upper rotating body
and including a supercharger, the internal-combustion engine being
configured to be controlled at a constant revolution speed, a
hydraulic pump coupled to the internal-combustion engine, a
hydraulic actuator to be driven by a hydraulic oil discharged from
the hydraulic pump, a control valve system including a plurality of
flow control valves for controlling a flow of the hydraulic oil
discharged from the hydraulic pump, and a controller that controls
an absorbing horsepower of the hydraulic pump, the method
comprising: increasing, by the controller, a boost pressure of the
supercharger before a load is applied to the hydraulic actuator by
controlling a specific flow control valve in the control valve
system to limit or block the flow of the hydraulic oil discharged
from the hydraulic pump and thereby increasing a discharge pressure
of the hydraulic pump.
11. The method as claimed in claim 10, wherein the controller
increases the absorbing horsepower of the hydraulic pump regardless
of whether a reaction force received by an end attachment from a
work object increases or decreases.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application filed under
35 U.S.C. 111(a) claiming benefit under 35 U.S.C. 120 and 365(c) of
PCT International Application No. PCT/JP2015/053771, filed on Feb.
12, 2015 and designated the U.S., which claims priority to Japanese
Patent Application No. 2014-033316, filed on Feb. 24, 2014. The
entire contents of the foregoing applications are incorporated
herein by reference.
BACKGROUND
[0002] Technical Field
[0003] An aspect of this disclosure relates to a shovel and a
method of controlling the shovel.
[0004] Description of Related Art
[0005] A turbocharger (turbo-supercharger) engine is often used as
an engine (internal combustion engine) for a hydraulic shovel. A
turbocharger uses an exhaust gas of an engine to rotate a turbine
and generate a pressure, and introduces the generated pressure into
an induction system of the engine to supercharge the engine and
increase the engine power.
[0006] When a boom is started to be driven during the operation of
a shovel, the hydraulic load increases and the engine load of an
engine having been driven at a constant revolution speed also
increases. When the engine load increases, to maintain the engine
revolution speed, the engine increases the engine power by
increasing the charging pressure (boost pressure) and the fuel
injection amount.
[0007] For example, to quickly respond to an increase in the engine
load, a related-art power control device increases the boost
pressure of a turbocharger engine and thereby increases the engine
power when an operation that may increase the engine load is
detected.
SUMMARY
[0008] In an aspect of this disclosure, there is provided a shovel
that includes a lower traveling body; an upper rotating body
mounted on the lower traveling body; an internal-combustion engine
that is mounted on the upper rotating body, includes a
supercharger, and is controlled at a constant revolution speed; a
hydraulic pump coupled to the internal-combustion engine; a
hydraulic actuator to be driven by a hydraulic oil discharged from
the hydraulic pump; a control valve system including multiple flow
control valves for controlling a flow of the hydraulic oil
discharged from the hydraulic pump; and a controller that controls
an absorbing horsepower of the hydraulic pump. The controller is
configured to increase a boost pressure of the supercharger before
a load is applied to the hydraulic actuator by controlling a
specific flow control valve in the control valve system to limit or
block the flow of the hydraulic oil discharged from the hydraulic
pump and thereby increasing a discharge pressure of the hydraulic
pump.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a side view of a shovel according to an embodiment
of the present invention;
[0010] FIG. 2 is a drawing illustrating an exemplary configuration
of a driving system of the shovel of FIG. 1;
[0011] FIG. 3 is a drawing illustrating an exemplary configuration
of a hydraulic system of the shovel of FIG. 1;
[0012] FIG. 4 is a graph illustrating an exemplary relationship
between the discharge pressure and the discharge rate of a main
pump;
[0013] FIG. 5 is a flowchart illustrating an exemplary
absorbing-horsepower increasing process;
[0014] FIG. 6 is a drawing illustrating temporal changes in
physical quantities observed when the absorbing-horsepower
increasing process of FIG. 5 is performed;
[0015] FIG. 7 is a flowchart illustrating another exemplary
absorbing-horsepower increasing process;
[0016] FIG. 8 is a drawing illustrating another exemplary
configuration of a hydraulic system of the shovel of FIG. 1;
[0017] FIG. 9 is a flowchart illustrating another exemplary
absorbing-horsepower increasing process; and
[0018] FIG. 10 is a drawing illustrating temporal changes in
physical quantities observed when the absorbing-horsepower
increasing process of FIG. 9 is performed.
DETAILED DESCRIPTION
[0019] The related-art power control device increases the boost
pressure when an increase in the hydraulic load is detected. That
is, the related-art power control device increases the boost
pressure after the hydraulic load increases to a certain level due
to an external force such as an excavation reaction force.
Accordingly, in a case where the hydraulic load rapidly increases
due to an external force such as an excavation reaction force with
respect to the engine power, the related-art power control device
cannot increase the boost pressure quickly enough to keep up with
the increase in the hydraulic load. This may result in, for
example, generation of black smoke due to incomplete combustion of
fuel and an engine power shortage, and may further result in an
engine stop.
[0020] An aspect of this disclosure provides a shovel and a method
of controlling the shovel that can increase the boost pressure
without delay.
[0021] Embodiments of the present invention are described below
with reference to the accompanying drawings.
[0022] First, a shovel, which is a construction machine, according
to an embodiment of the present invention is described with
reference to FIG. 1. FIG. 1 is a side view of the shovel according
to the present embodiment. As illustrated by FIG. 1, the shovel
includes a lower traveling body 1 on which an upper rotating body
is mounted via a rotating mechanism 2. A boom 4 is attached to the
upper rotating body 3. An arm 5 is attached to an end of the boom
4, and a bucket 6, which is an end attachment, is attached to an
end of the arm 5. The boom 4, the arm 5, and the bucket 6 are
hydraulically-driven by a boom cylinder 7, an arm cylinder 8, and a
bucket cylinder 9, respectively. The upper rotating body 3 includes
a cabin 10 and a power source such as an engine 11.
[0023] FIG. 2 is a drawing illustrating an exemplary configuration
of a driving system of the shovel of FIG. 1. In FIG. 2, a
mechanical driving system is represented by double lines,
high-pressure hydraulic lines are represented by bold-solid lines,
pilot lines are represented by dashed lines, and an electric
control system is represented by dotted lines.
[0024] The driving system of the shovel includes an engine 11, a
regulator 13, a main pump 14, a pilot pump 15, a control valve
system 17, an operating device 26, a pressure sensor 29, a
controller 30, a pressure control valve 31, an atmospheric pressure
sensor P1, a discharge pressure sensor P2, a boost pressure sensor
P3, and a switcher 50.
[0025] The engine 11 is a driving source of the shovel. In the
present embodiment, the engine 11 is, for example, an
internal-combustion engine such as a diesel engine that is
configured to maintain a predetermined revolution speed. The output
shaft of the engine 11 is connected to input shafts of the main
pump 14 and the pilot pump 15. In the present embodiment, a
supercharger 11a is provided on the engine 11. For example, the
supercharger 11a may be configured to use an exhaust gas of the
engine 11 to rotate a turbine and drive a centrifugal compressor by
the rotational force of the turbine to increase an intake pressure
(to generate a boost pressure). The supercharger 11a may also be
configured to generate a boost pressure by using the rotation of
the output shaft of the engine 11. With this configuration, the
engine 11 can increase the boost pressure and increase the engine
power according to an increase in the load.
[0026] The main pump 14 supplies a hydraulic oil via a
high-pressure hydraulic line to the control valve system 17 and may
be implemented by, for example, a variable-displacement swash-plate
hydraulic pump.
[0027] The regulator 13 controls the discharge rate of the main
pump 14. In the present embodiment, the regulator 13 adjusts the
inclination angle of a swash plate of the main pump 14 according
to, for example, the discharge pressure of the main pump 14 or a
control signal from the controller 30 to control the discharge rate
of the main pump 14.
[0028] The pilot pump 15 supplies a hydraulic oil via pilot lines
to hydraulic control devices including the operating device 26 and
the pressure control valve 31 and may be implemented by, for
example, a fixed-displacement hydraulic pump.
[0029] The control valve system 17 is a hydraulic control device
that controls the hydraulic system of the shovel. More
specifically, the control valve system 17 includes multiple flow
control valves that control the flow of the hydraulic oil
discharged from the main pump 14. With the flow control valves, the
control valve system 17 selectively supplies the hydraulic oil
discharged from the main pump 14 to one or more hydraulic
actuators. The hydraulic actuators include the boom cylinder 7, the
arm cylinder 8, the bucket cylinder 9, a traveling hydraulic motor
1A (left), a traveling hydraulic motor 1B (right), and a rotating
hydraulic motor 2A.
[0030] The operating device 26 is used by an operator to operate
the hydraulic actuators. In the present embodiment, the operating
device 26 supplies the hydraulic oil discharged from the pilot pump
15 via pilot lines to pilot ports of the flow control valves
corresponding to the hydraulic actuators. The pressure (pilot
pressure) of the hydraulic oil supplied to each pilot port
corresponds to the operation direction and the operation amount of
a lever or a pedal (not shown) of the operating device 26
corresponding to one of the hydraulic actuators.
[0031] The pressure sensor 29 detects operations performed by the
operator using the operating device 26. In the present embodiment,
the pressure sensor 20 detects pressures representing the operation
direction and the operation amount of a lever or a pedal of the
operating device 26 corresponding to each hydraulic actuator, and
outputs the detected pressures to the controller 30. Operations
performed using the operating device 26 may also be detected by a
sensor other than a pressure sensor.
[0032] The controller 30 is a control device that controls the
shovel. In the present embodiment, the controller 30 may be
implemented by, for example, a computer including a central
processing unit (CPU), a random access memory (RAM), and a
read-only memory (ROM). The controller 30 reads programs
corresponding to a boost-pressure increase determiner 300 and an
absorbing-horsepower controller 301 from the ROM, loads the read
programs into the RAM, and causes the CPU to perform processes
corresponding to the programs.
[0033] Specifically, the controller 30 receives signals output from
the pressure sensor 29, the atmospheric pressure sensor P1, the
discharge pressure sensor P2, the boost pressure sensor P3, and the
switcher 50. Based on the received signals, the boost-pressure
increase determiner 300 and the absorbing-horsepower controller 301
perform the corresponding processes. Then, the controller 30
outputs control signals corresponding to the results of processes
performed by the boost-pressure increase determiner 300 and the
absorbing-horsepower controller 301 to, for example, the regulator
13 and the pressure control valve 31 as necessary.
[0034] More specifically, the boost-pressure increase determiner
300 determines whether it is necessary to increase the boost
pressure. When the boost-pressure increase determiner 300
determines that it is necessary to increase the boost pressure, the
absorbing-horsepower controller 301 controls the pressure control
valve 31 to increase the discharge pressure of the main pump 14.
Also, the absorbing-horsepower controller 301 may be configured to
increase the discharge rate of the main pump 14 in addition to the
discharge pressure by adjusting the regulator 13.
[0035] The pressure control valve 31 operates according to a
command output from the controller 30. In the present embodiment,
the pressure control valve 31 is a solenoid pressure reducing valve
that adjusts a control pressure introduced from the pilot pump 15
into a pilot port of a specific flow control valve in the control
valve system 17 according to a current command output by the
controller 30. The controller 30 operates the specific flow control
valve to limit the flow of the hydraulic oil discharged from the
main pump 14 and thereby increase the discharge pressure of the
main pump 14.
[0036] Thus, the controller 30 increases the discharge pressure of
the main pump 14 to voluntarily increase the absorbing horsepower
of the main pump 14. Also, the controller 30 may be configured to
increase the discharge rate of the main pump 14 in addition to the
discharge pressure to voluntarily increase the absorbing horsepower
of the main pump 14. Here, "to voluntarily increase the absorbing
horsepower" means increasing the absorbing horsepower independently
of an external force such as an excavation reaction force, i.e.,
increasing the absorbing horsepower even when there is no increase
in the hydraulic load.
[0037] The atmospheric pressure sensor P1 detects an atmospheric
pressure and outputs the detected atmospheric pressure to the
controller 30. The discharge pressure sensor P2 detects a discharge
pressure of the main pump and outputs the detected discharge
pressure to the controller 30. The boost pressure sensor P3 detects
a boost pressure generated by the supercharger 11a and outputs the
detected boost pressure to the controller 30.
[0038] The switcher 50 is a switch that activates and deactivates a
function (which is hereafter referred to as an
"absorbing-horsepower increasing function") of the controller 30
for voluntarily increasing the absorbing horsepower of the main
pump 14. The switcher 50 may be disposed in, for example, the cabin
10. The operator turns on the switcher 50 to activate the
absorbing-horsepower increasing function and turns off the switcher
to deactivate the absorbing-horsepower increasing function. More
specifically, when the switcher 50 is turned off, the controller 30
stops execution of the boost-pressure increase determiner 300 and
the absorbing-horsepower controller 301 and deactivates their
functions.
[0039] A mechanism for changing the absorbing horsepower of the
main pump 14 is described below with reference to FIG. 3. FIG. 3 is
a drawing illustrating an exemplary configuration of a hydraulic
system of the shovel of FIG. 1. In FIG. 3, similarly to FIG. 2, a
mechanical driving system is represented by double lines,
high-pressure hydraulic lines are represented by bold-solid lines,
pilot lines are represented by dashed lines, and an electric
control system is represented by dotted lines.
[0040] As illustrated by FIG. 3, the hydraulic system is configured
to circulate a hydraulic oil from main pumps 14L and 14R driven by
the engine 11, via center bypass pipe lines 40L and 40R and
parallel pipe lines 42L and 42R, to a hydraulic oil tank. The main
pumps 14L and 14R correspond to the main pump 14 of FIG. 2.
[0041] The center bypass pipe line 40L is a high-pressure hydraulic
line that passes through flow control valves 171, 173, 175, and 177
disposed in the control valve system 17. The center bypass pipe
line 40R is a high-pressure hydraulic line that passes through flow
control valves 172, 174, 176, and 178 disposed in the control valve
system 17.
[0042] The flow control valve 171 is a spool valve that supplies
the hydraulic oil discharged from the main pump 14L to the
traveling hydraulic motor 1A (left) and changes the flow of the
hydraulic oil to discharge the hydraulic oil from the traveling
hydraulic motor 1A (left) into the hydraulic oil tank.
[0043] The flow control valve 172 is a spool valve that supplies
the hydraulic oil discharged from the main pump 14R to the
traveling hydraulic motor 1B (right) and changes the flow of the
hydraulic oil to discharge the hydraulic oil from the traveling
hydraulic motor 1B (right) into the hydraulic oil tank.
[0044] The flow control valve 173 is a spool valve that supplies
the hydraulic oil discharged from the main pump 14L to the rotating
hydraulic motor 2A and changes the flow of the hydraulic oil to
discharge the hydraulic oil from the rotating hydraulic motor 2A
into the hydraulic oil tank.
[0045] The flow control valve 174 is a spool valve that supplies
the hydraulic oil discharged from the main pump 14R to the bucket
cylinder 9 and discharges the hydraulic oil from the bucket
cylinder 9 into the hydraulic oil tank.
[0046] The flow control valves 175 and 176 are spool valves that
supply the hydraulic oil discharged from the main pumps 14L and 14R
to the boom cylinder 7 and change the flow of the hydraulic oil to
discharge the hydraulic oil from the boom cylinder 7 into the
hydraulic oil tank. In the present embodiment, the flow control
valve 175 operates only when a raising operation of the boom 4 is
performed and does not operate when a lowering operation of the
boom 4 is performed. More specifically, when a raising operation of
the boom 4 is performed, the flow control valve 175 moves from a
center valve position (C) toward a right valve position (R). On the
other hand, even when a lowering operation of the boom 4 is
performed, the flow control valve 175 does not move from the center
valve position (C) toward a left valve position (L) but remains at
the center valve position (C). Accordingly, the left valve position
(L) of the flow control valve 175 can be used for other purposes.
The controller 30 uses the left valve position (L) of the flow
control valve 175 to activate the absorbing-horsepower increasing
function.
[0047] The flow control valves 177 and 178 are spool valves that
supply the hydraulic oil discharged from the main pumps 14L and 14R
to the arm cylinder 8 and change the flow of the hydraulic oil to
discharge the hydraulic oil from the arm cylinder 8 into the
hydraulic oil tank.
[0048] The parallel pipe line 42L is a high-pressure hydraulic line
that extends parallel to the center bypass pipe line 40L. When the
flow of the hydraulic oil passing through the center bypass pipe
line 40L is limited or blocked by one of the flow control valves
171, 173, and 175, the parallel pipe line 42L supplies the
hydraulic oil to a further downstream flow control valve. The
parallel pipe line 42R is a high-pressure hydraulic line that
extends parallel to the center bypass pipe line 40R. When the flow
of the hydraulic oil passing through the center bypass pipe line
40R is limited or blocked by one of the flow control valves 172,
174, and 176, the parallel pipe line 42R supplies the hydraulic oil
to a further downstream flow control valve.
[0049] In the present embodiment, the cross-sectional area of the
parallel pipe line 42L is less than the cross-sectional area of the
center bypass pipe line 40L. Accordingly, compared with the center
bypass pipe line 40L, the parallel pipe line 42L allows the
hydraulic oil to flow at a lower rate. When the flow of the
hydraulic oil passing through the center bypass pipe line 40L is
limited or blocked and the amount of the hydraulic oil passing
through the parallel pipe line 42L increases, the discharge
pressure of the main pump 14L increases, and the flow rate of the
hydraulic oil that reaches a negative control throttle 18L
decreases. The above descriptions also apply to the center bypass
pipe line 40R and the parallel pipe line 42R.
[0050] Regulators 13L and 13R adjust the inclination angles of
swash plates of the main pumps 14L and 14R according to the
discharge pressures of the main pumps 14L and 14R to control the
discharge rates of the main pumps 14L and 14R. The regulators 13L
and 13R correspond to the regulator 13 of FIG. 2. More
specifically, when the discharge pressures of the main pumps 14L
and 14R become greater than or equal to a predetermined value, the
regulators 13L and 13R adjust the inclination angles of the swash
plates of the main pumps 14L and 14R to decrease the discharge
rates of the main pumps 14L and 14R. This is to prevent the
absorbing horsepower of the main pump 14, which is represented by a
product of the discharge pressure and the discharge rate, from
exceeding the output horsepower of the engine 11. Hereafter, this
control is referred to as a "full horsepower control".
[0051] An arm operation lever 26A is an example of the operating
device 26 and is used to operate the arm 5. The arm operation lever
26A introduces a control pressure corresponding to a lever
operation amount to the pilot ports of the flow control valves 177
and 178 by using the hydraulic oil discharged from the pilot pump
15. More specifically, when the arm operation lever 26A is operated
in an arm closing direction, the hydraulic oil is introduced into a
right pilot port 177R of the flow control valve 177 and into a left
pilot port 178L of the flow control valve 178. On the other hand,
when the arm operation lever 26A is operated in an arm opening
direction, the hydraulic oil is introduced into a left pilot port
177L of the flow control valve 177 and into a right pilot port 178R
of the flow control valve 178.
[0052] A boom operation lever 26B is an example of the operating
device 26 and is used to operate the boom 4. The boom operation
lever 26B introduces a control pressure corresponding to a lever
operation amount to the pilot ports of the flow control valves 175
and 176 by using the hydraulic oil discharged from the pilot pump
15. More specifically, when the boom operation lever 26B is
operated in a boom raising direction, the hydraulic oil is
introduced into a right pilot port 175R of the flow control valve
175 and into a left pilot port 176L of the flow control valve 176.
On the other hand, when the boom operation lever 26B is operated in
a boom lowering direction, the hydraulic oil is not introduced into
a left pilot port 175L of the flow control valve 175 but is
introduced into only a right pilot port 176R of the flow control
valve 176.
[0053] Pressure sensors 29A and 29B are examples of the pressure
sensor 29. The pressure sensors 29A and 29B detect pressures
representing operations performed by the operator on the arm
operation lever 26A and the boom operation lever 26B, and output
the detected pressures to the controller 30. Each operation is
indicated by, for example, a lever operation direction and a lever
operation amount (lever operation angle).
[0054] Right and left driving levers (or pedals), a bucket
operation lever, and a rotation operation lever (which are not
shown) are operation devices used to drive the lower traveling body
1, to open and close a the bucket 6, and to rotate the upper
rotating body 3, respectively. Similarly to the arm operation lever
26A, each of these operation devices introduces a control pressure
corresponding to a lever operation amount (or a pedal operation
amount) to one of right and left pilot ports of a flow control
valve corresponding to one of the hydraulic actuators by using the
hydraulic oil discharged from the pilot pump 15. Also, similarly to
the pressure sensor 29A, a pressure sensor corresponding to each of
these operation devices detects a pressure representing an
operation performed by the operator on the corresponding operation
device and outputs the detected pressure to the controller 30.
[0055] The controller 30 receives pressures detected by pressure
sensors such as the pressure sensor 29A and outputs control signals
to the regulators 13L and 13R as necessary to change the discharge
rates of the main pumps 14L and 14R.
[0056] The pressure control valve 31 adjusts a control pressure
introduced from the pilot pump 15 into the left pilot port 175L of
the flow control valve 175 according to a current command output
from the controller 30. Thus, the movement of the flow control
valve 175 to the left valve position (L) is not caused by any of
the operation levers including the boom operation lever 26B, and is
solely caused by a pilot pressure generated by the pressure control
valve 31. Also, the pressure control valve 31 can adjust the
control pressure such that the flow control valve 175 can be
stopped at two positions, a first intermediate position and a
second intermediate position, when the flow control valve 175 is
moved from the center valve position (C) to the left valve position
(L). The first intermediate position is a valve position at which
the opening area of the center bypass pipe line 40L becomes 70% of
the maximum opening area, and the second intermediate position is a
valve position at which the opening area of the center bypass pipe
line 40L becomes 30% of the maximum opening area. Here, the opening
area becomes the maximum opening area when the flow control valve
175 is at the valve position (C). Also, the opening area becomes 0%
when the flow control valve 175 is at the valve position (L).
[0057] A negative control employed by the hydraulic system of FIG.
3 is described below.
[0058] The center bypass pipe lines 40L and 40R include negative
control throttles 18L and 18R between the most downstream flow
control valves 177 and 178 and the hydraulic oil tank. The flow of
the hydraulic oil discharged from the main pumps 14L and 14R is
limited by the negative control throttles 18L and 18R. The negative
control throttles 18L and 18R generate control pressures (which are
hereafter referred to as "negative control pressures") to control
the regulators 13L and 13R.
[0059] Negative control pressure pipe lines 41L and 41R indicated
by dashed lines are pilot lines for transmitting negative control
pressures generated upstream of the negative control throttles 18L
and 18R to the regulators 13L and 13R.
[0060] The regulators 13L and 13R adjust the inclination angles of
the swash plates of the main pumps 14L and 14R according to the
negative control pressures to control the discharge rates of the
main pumps 14L and 14R. The regulators 13L and 13R decrease the
discharge rates of the main pumps 14L and 14R as the negative
control pressures increase, and increase the discharge rates of the
main pumps 14L and 14R as the negative control pressures
decrease.
[0061] Specifically, as illustrated in FIG. 3, when none of the
hydraulic actuators of the shovel is being operated (this state is
hereafter referred to as a "standby mode"), the hydraulic oil
discharged from the main pumps 14L and 14R pass through the center
bypass pipe lines 40L and 40R and reach the negative control
throttles 18L and 18R. In this case, the flow of the hydraulic oil
discharged from the main pumps 14L and 14R increases the negative
control pressures generated upstream of the negative control
throttles 18L and 18R. As a result, the regulators 13L and 13R
decrease the discharge rates of the main pumps 14L and 14R to a
minimum allowable discharge rate to reduce a pressure loss (pumping
loss) that occurs when the discharged hydraulic oil passes through
the center bypass pipe lines 41L and 40R.
[0062] On the other hand, when a hydraulic actuator is activated,
the hydraulic oil discharged from the main pumps 14L and 14R flows
via the corresponding flow control valve into the operated
hydraulic actuator. In this case, the amount of the hydraulic oil
that is discharged from the main pumps 14L and 14R and reaches the
negative control throttles 18L and 18R decreases or becomes zero,
and the negative control pressures generated upstream of the
negative control throttles 18L and 18R decrease. As a result, the
regulators 13L and 13R receiving the decreased negative control
pressures increase the discharge rates of the main pumps 14L and
14R to supply a sufficient amount of the hydraulic oil to the
operated hydraulic actuator and thereby stably drive the operated
hydraulic actuator.
[0063] With the above configuration, the hydraulic system of FIG. 3
can reduce unnecessary energy consumption of the main pumps 14L and
14R during the standby mode. Here, the unnecessary energy
consumption includes the pumping loss that occurs when the
hydraulic oil discharged from the main pumps 14L and 14R passes
through the center bypass pipe lines 40L and 40R.
[0064] Also, the hydraulic system of FIG. 3 is configured such that
a sufficient amount of the hydraulic oil can be reliably supplied
from the main pumps 14L and 14R to a hydraulic actuator to be
activated.
[0065] Next, a relationship between the full horsepower control by
the regulator 13 and the negative control is described with
reference to FIG. 4. FIG. 4 is a graph illustrating an exemplary
relationship between a discharge rate Q and a discharge pressure P
of the main pump 14.
[0066] The regulator 13 controls the discharge rate Q of the main
pump 14 according to a full power control curve indicated by a
solid line in FIG. 4. Specifically, the regulator 13 decreases the
discharge rate Q as the discharge pressure P increases so that the
absorbing horsepower of the main pump 14 does not exceed the engine
output. Also, apart from the full power control, the regulator 13
controls the discharge rate Q of the main pump 14 according to a
negative control pressure. Specifically, the regulator 13 decreases
the discharge rate Q as the negative control pressure increases.
When the negative control pressure further increases and exceeds a
predetermined value, the regulator 13 decreases the discharge rate
Q to a negative control flow rate Qn that is the minimum allowable
discharge rate. As a result, the negative control pressure
decreases to a predetermined pressure Pn. However, the regulator 13
does not increase the discharge rate Q and maintains the negative
control flow rate Qn until the negative control pressure becomes
lower than a negative control cancellation pressure Pr
(<Pn).
[0067] Also in the present embodiment, apart from the full power
control and the negative control, the regulator 13 controls the
discharge rate Q of the main pump 14 according to a control signal
from the controller 30. Specifically, the regulator 13 increases
and decreases the discharge rate Q according to a control signal
output by the controller 30 when the boost-pressure increase
determiner 300 determines that the boost pressure needs to be
increased.
[0068] More specifically, the boost-pressure increase determiner
300 determines that the boost pressure needs to be increased when,
for example, the shovel is in the standby mode. In this case, the
absorbing-horsepower controller 301 controls the pressure control
valve 31 to increase the discharge pressure of the main pump 14. In
the present embodiment, the absorbing-horsepower controller 301
introduces the hydraulic oil into the left pilot port 175L of the
flow control valve 175 to cause the flow control valve 175 to move
from the center valve position (C) toward the left valve position
(L). The flow control valve 175 moved toward the left valve
position (L) limits the flow rate of the hydraulic oil flowing
through the center bypass pipe line 40L and increases the discharge
pressure of the main pump 14L. As a result, the absorbing
horsepower of the main pump 14 increases and the engine load
increases, and the absorbing-horsepower controller 301 can increase
the boost pressure. Also, the absorbing-horsepower controller 301
monitors whether the boost pressure generated by the supercharger
11a has reached a desired boost pressure based on the output of the
boost pressure sensor P3.
[0069] Then, when the current boost pressure is not at the desired
boost pressure, the absorbing-horsepower controller 301 outputs a
control signal to the regulator 13L to adjust the regulator 13L and
thereby adjust the discharge rate of the main pump 14L in addition
to the discharge pressure. More specifically, when the current
boost pressure is lower than the desired boost pressure, the
absorbing-horsepower controller 301 may adjust the regulator 13L to
increase the discharge rate of the main pump 14L and increase the
absorbing horsepower of the main pump 14L. Also, when the current
boost pressure is higher than the desired boost pressure, the
absorbing-horsepower controller 301 may adjust the regulator 13L to
decrease the discharge rate of the main pump 14L and decrease the
absorbing horsepower of the main pump 14L.
[0070] Next, a process (which is hereafter referred to as an
"absorbing-horsepower increasing process") performed by the
controller 30 to voluntarily increase the absorbing horsepower of
the main pump 14 is described with reference to FIG. 5. FIG. 5 is a
flowchart illustrating an absorbing-horsepower increasing process.
The controller 30 repeats the absorbing-horsepower increasing
process at predetermined intervals. In the present embodiment,
because the switcher 50 is manually turned on, the controller 30
can activate the boost-pressure increase determiner 300 and the
absorbing-horsepower controller 301. Here, in an environment such
as a high altitude where the atmospheric pressure is comparatively
low, it is difficult to increase the boost pressure after an
increase in the hydraulic load is detected as in an environment
where the atmospheric pressure is comparatively high. This may
result in, for example, generation of black smoke due to incomplete
combustion of fuel and an engine power shortage, and may further
result in an engine stop.
[0071] First, the boost-pressure increase determiner 300 of the
controller 300 determines whether it is necessary to increase the
boost pressure. In the present embodiment, the boost-pressure
increase determiner 300 determines whether the shovel is in the
standby mode (step S1). Also in the present embodiment, the
boost-pressure increase determiner 300 determines whether the
shovel is in the standby mode based on whether the discharge
pressure of the main pump 14 is greater than or equal to a
predetermined pressure. For example, the boost-pressure increase
determiner 300 determines that the shovel is in the standby mode,
i.e., the boost pressure needs to be increased, when the discharge
pressure of the main pump 14 is less than the predetermined
pressure. Also, the boost-pressure increase determiner 300 may
determine whether the shovel is in the standby mode based on the
pressures of the hydraulic actuators.
[0072] When the boost-pressure increase determiner 300 determines
that the shovel is in the standby mode (no hydraulic load is being
applied) (YES at step S1), the absorbing-horsepower controller 301
of the controller 30 increases the absorbing horsepower of the main
pump 14 to increase the boost pressure (step S2). In the present
embodiment, the absorbing-horsepower controller 301 outputs a
current command to the pressure control valve 31 to increase the
control pressure introduced into the left pilot port 175L of the
flow control valve 175. When the control pressure introduced into
the left pilot port 175L increases, the flow control valve 175
moves from the center valve position (C) toward the left valve
position (L) to limit the flow rate of the hydraulic oil flowing
through the center bypass pipe line 40L and increase the discharge
pressure of the main pump 14L. Also, the flow control valve 175
causes the amount of the hydraulic oil reaching the negative
control throttle 18L to decrease or become zero, and thereby
decreases the negative control pressure generated upstream of the
negative control throttle 18L. As a result, the regulator 13L
receiving the decreased negative control pressure increases the
discharge rate of the main pump 14L. Thus, the absorbing-horsepower
controller 301 increases the discharge pressure and the discharge
rate of the main pump 14L and thereby increases the absorbing
horsepower of the main pump 14L. With this configuration, the
absorbing-horsepower controller 301 can apply a load sufficient to
increase the boost pressure to the engine 11 even in the standby
mode. Here, when the absorbing horsepower of the main pump 14L
increases, the rotational load of the engine 11 increases and
therefore the engine 11 increases the fuel injection amount to
maintain a predetermined revolution speed. The increase in the fuel
injection amount results in an increase in the exhaust pressure, an
increase in the rotational speed of the turbine, and an increase in
the rotational speed of the centrifugal compressor, which further
result in an increase in the boost pressure.
[0073] Thereafter, the absorbing-horsepower controller 301
fine-tunes the absorbing horsepower of the main pump 14L while
monitoring whether the boost pressure has reached a desired boost
pressure based on the output of the boost pressure sensor P3 (step
S3). In the present embodiment, the absorbing-horsepower controller
301 outputs a control signal to the regulator 13L. When receiving
the control signal, the regulator 13L stops adjusting the
inclination angle of the swash plate based on the negative control
pressure. Then, the regulator 13L adjusts the inclination angle of
the swash plate based on the control signal to increase or decrease
the discharge rate of the main pump 14L. Thus, the
absorbing-horsepower controller 301 can achieve the desired boost
pressure by fine-tuning the absorbing horsepower of the main pump
14L increased by using the pressure control valve 31 and thereby
fine-tuning the boost pressure. However, the absorbing-horsepower
controller 301 may omit the fine-tuning of the absorbing horsepower
of the main pump 14L by the regulator 13L.
[0074] On the other hand, when the boost-pressure increase
determiner 300 determines that the shovel is not in the standby
mode (a hydraulic load is being applied) (NO at step S1) and the
absorbing horsepower of the main pump 14 is being increased to
increase the boost pressure, the absorbing-horsepower controller
301 stops increasing the absorbing horsepower (step S4). That is,
in this case, because the activation of a hydraulic actuator
increases the absorbing horsepower of the main pump 14 and
increases the boost pressure, it is not necessary to voluntarily
increase the absorbing horsepower of the main pump 14L. In the
present embodiment, if the absorbing-horsepower controller 301 is
outputting a current command to the pressure control valve 31, the
absorbing-horsepower controller 301 stops outputting the current
command. Also, if the absorbing-horsepower controller 301 is
increasing the control pressure introduced into the left pilot port
175L of the flow control valve 175, the absorbing-horsepower
controller 301 stops increasing the control pressure. When the
absorbing-horsepower controller 301 stops increasing the control
pressure introduced into the left pilot port 175L, the flow control
valve 175 moves from the left valve position (L) toward the center
valve position (C). As a result, the flow control valve 175 stops
limiting the flow rate of the hydraulic oil flowing through the
center bypass pipe line 40L and stops increasing the discharge
pressure of the main pump 14L. Compared with a case where the flow
control valve 175 is moved toward the left valve position (L),
moving the flow control valve 175 toward the center valve position
(C) increases the amount of the hydraulic oil reaching the negative
control throttle 18L and thereby increases the negative control
pressure generated upstream of the negative control throttle 18L.
As a result, the regulator 13L receiving the increased negative
control pressure decreases the discharge rate of the main pump 14L.
Thus, the absorbing-horsepower controller 301 stops increasing the
discharge pressure and the discharge rate of the main pump 14L and
thereby stops increasing the absorbing horsepower of the main pump
14L. Here, when the absorbing-horsepower controller 301 stops
increasing the absorbing horsepower of the main pump 14L, the
rotational load of the engine 11 returns to a previous level before
the increase of the absorbing horsepower and therefore the engine
11 decreases the fuel injection amount to a previous level before
the increase of the absorbing horsepower. When the fuel injection
amount returns to the previous level before the increase of the
absorbing horsepower, the exhaust pressure, the rotational speed of
the turbine, and the rotational speed of the centrifugal compressor
return to previous levels before the increase of the absorbing
horsepower, and the boost pressure also returns to a previous level
before the increase of the absorbing horsepower.
[0075] Thus, the controller 30 increases the absorbing horsepower
of the main pump 14 during the standby mode. With this
configuration, the controller 30 can voluntarily apply a
predetermined load to the engine 11 and increase the boost pressure
of the supercharger 11a even when no hydraulic load is being
applied by an external force such as an excavation reaction force.
That is, the controller 30 can increase the boost pressure by a
predetermined amount before the hydraulic load increases due to an
external force without directly controlling the engine 11 and the
supercharger 11a. Even in an environment where the boost pressure
cannot be increased quickly due to a low atmospheric pressure, this
configuration makes it possible to generate a boost pressure
corresponding to an increasing hydraulic load before a problem such
as a decrease in the engine revolution speed (a decrease in
responsiveness and performance) or an engine stop occurs.
[0076] Temporal changes in physical quantities, which are observed
when the absorbing-horsepower increasing process is performed, are
described with reference to FIG. 6. FIG. 6 is a drawing
illustrating temporal changes in physical quantities including the
atmospheric pressure, the lever operation amount, the hydraulic
load (absorbing horsepower), the boost pressure, the fuel injection
amount, and the engine revolution speed arranged in this order from
the top. Each dashed line in FIG. 6 indicates a temporal change in
a case where the shovel is at low altitude (in a comparatively-high
atmospheric pressure environment) and the absorbing-horsepower
increasing process is not performed. Each dashed-dotted line in
FIG. 6 indicates a temporal change in a case where the shovel is at
high altitude (in a comparatively-low atmospheric pressure
environment) and the absorbing-horsepower increasing process is not
performed. Also, each solid line in FIG. 6 indicates a temporal
change in a case where the shovel is at high altitude (in a
comparatively-low atmospheric pressure environment) and the
absorbing-horsepower increasing process is performed.
[0077] In FIG. 6, it is assumed that a lever is operated at a time
t1 to move, for example, the arm 5 for excavation.
[0078] First, for comparison, temporal changes in physical
quantities in the case where the shovel is at low altitude (in a
comparatively-high atmospheric pressure environment) and the
absorbing-horsepower increasing process is not performed and in the
case where the shovel is at high altitude (in a comparatively-low
atmospheric pressure environment) and the absorbing-horsepower
increasing process is not performed.
[0079] At the time t1, an operation of the arm operation lever is
started to perform excavation. The operation amount of the arm
operation lever (an angle the arm operation lever is tilted)
increases from the time t1 to a time t2, and becomes constant at
the time t2. That is, the arm operation lever is started to be
tilted at the time t1, and the angle of the arm operation lever is
fixed at the time t2. When the operation of the arm operation lever
is started at the time t1, the arm 5 starts to move. At the time
t2, the arm operation lever is fully tilted.
[0080] From the time t2 at which the arm operation lever is fully
tilted, the discharge pressure of the main pump 14 starts to
increase due to a load applied to the arm 5, and the hydraulic load
of the main pump 14 starts to increase. That is, the hydraulic load
of the main pump 14 starts to increase at around the time t2 as
indicated by the dashed line and the dashed-dotted line. The
hydraulic load of the main pump 14 corresponds to the load of the
engine 11, and therefore the load of the engine 11 also increases
along with the hydraulic load of the main pump 14. In the case
where the shovel is at low altitude (in a comparatively-high
atmospheric pressure environment), the revolution speed of the
engine 11 is maintained at a predetermined revolution speed as
indicated by the dashed line. On the other hand, in the case where
the shovel is at high altitude (in a comparatively-low atmospheric
pressure environment), the revolution speed of the engine 11 starts
to decrease sharply at a point slightly after the time t2 as
indicted by the dashed-dotted line. This is because there is a
delay in the increase of the boost pressure in a comparatively-low
atmospheric pressure environment, and an engine power corresponding
to the load of the engine 11 cannot be achieved.
[0081] More specifically, when the load of the engine increases,
the engine 11 is normally controlled to increase the fuel injection
amount. This in turn increases the boost pressure, improves the
combustion efficiency of the engine 11, and increases the power of
the engine 11. However, while the boost pressure is low, the
increase in the fuel consumption amount is limited and the
combustion efficiency of the engine 11 cannot be sufficiently
improved. As a result, an engine power corresponding to the load of
the engine 11 is not achieved and the revolution speed of the
engine 11 decreases.
[0082] For this reason, when the shovel is at high altitude (in a
comparatively-low atmospheric pressure environment), the operator
turns on the switcher 50 to activate the absorbing-horsepower
increasing function. In response, the controller 30 performs the
absorbing-horsepower increasing process to increase the boost
pressure before a lever operation is performed.
[0083] Next, temporal changes in physical quantities in the case
where the shovel is at high altitude (in a comparatively-low
atmospheric pressure environment) and the absorbing-horsepower
increasing process is performed are described with reference to
FIG. 6. In FIG. 6, solid lines indicate temporal changes in
physical quantities in the case where the shovel is at high
altitude (in a comparatively-low atmospheric pressure environment)
and the absorbing-horsepower increasing process is performed.
[0084] As described above, at the time t1, the operator starts to
operate the arm operation lever to perform excavation. The
operation amount of the arm operation lever (an angle the arm
operation lever is tilted) increases from the time t1 to the time
t2, and becomes constant at the time t2. That is, the arm operation
lever is started to be tilted at the time t1, and the angle of the
arm operation lever is fixed at the time t2. When the operation of
the arm operation lever is started at the time t1, the arm 5 starts
to move. At the time t2, the arm operation lever is fully
tilted.
[0085] When the absorbing-horsepower increasing process is
performed, the controller 30 increases the absorbing horsepower of
the main pump 14 before the time t1, i.e., before the lever
operation is performed. Accordingly, the engine 11 is controlled to
increase the fuel injection amount to maintain the engine
revolution speed at the predetermined revolution speed. As a
result, the boost pressure is at a comparatively high level as in
the case where the shovel is at low altitude (in a
comparatively-high atmospheric pressure environment). That is, at
the time t2 at which the arm operation lever is fully tilted, the
boost pressure is at a level that can be quickly increased to a
desired level.
[0086] Thus, the controller 30 increases the absorbing horsepower
of the main pump 14 to apply a load to the engine 11 in advance so
that the boost pressure can be quickly increased to a desired level
after the time t2 at which the hydraulic load starts to
increase.
[0087] After the time t2, the hydraulic load increases and the load
of the engine 11 increases. As a result, the engine 11 is
controlled to further increase the fuel injection amount, and the
fuel consumption gradually increases. At this stage, the fuel
consumption increases only by an amount corresponding to the
increase in the hydraulic load. This is because the engine
revolution speed is already maintained at the predetermined
revolution speed and fuel consumption for increasing the engine
revolution speed is not necessary. At a time t3, because the boost
pressure is already greater than or equal to a predetermined value,
the engine 11 is in a condition to be able to efficiently increase
the engine output even when the hydraulic load increases.
[0088] As described above, by increasing the absorbing horsepower
of the main pump 14 and applying a load to the engine 11 before a
lever operation is performed, it is possible to start increasing
the boost pressure before the hydraulic load starts to
increase.
[0089] Here, as described above, in a comparatively-high
atmospheric pressure environment, the boost pressure (indicated by
the dashed line) is already at a comparatively high level at the
time t1 without performing the absorbing horsepower increasing
process.
[0090] Therefore, without the need to perform the absorbing
horsepower increasing process, the supercharger 11a is in a
condition to be able to quickly increase the boost pressure. Also,
the engine 11 is in a condition to be able to supply a driving
power corresponding to a hydraulic load caused by an external force
without experiencing a problem such as a decrease in the engine
revolution speed or an engine stop.
[0091] However, when the absorbing horsepower increasing process is
not performed in a comparatively-low atmospheric pressure
environment, the boost pressure (indicated by the dashed-dotted
line) is still at a comparatively low level even at the time t2.
Also, because the atmospheric pressure is comparatively low, the
supercharger 11a cannot quickly increase the boost pressure. More
specifically, until the time t3, the supercharger 11a cannot
achieve a sufficient boost pressure and the engine 11 cannot
sufficiently increase the fuel injection amount.
[0092] As a result, the engine 11 cannot output a driving power
that is sufficient to maintain the engine revolution speed at a
constant level, the engine revolution speed (indicated by the
dashed-dotted line) decreases, and the engine 11 may stop without
being able to increase the engine revolution speed.
[0093] For this reason, in a comparatively-low atmospheric pressure
environment, the controller 30 performs the absorbing-horsepower
increasing process to increase the absorbing horsepower of the main
pump 14 before the time t1, i.e., before the lever operation is
performed. Accordingly, the hydraulic load representing the
absorbing horsepower of the main pump 14 is at a comparatively high
level, and the boost pressure (indicated by the solid line) is also
at a comparatively high level already at the time t2.
[0094] As a result, even in the comparatively-low atmospheric
pressure environment, the supercharger 11a can quickly increase the
boost pressure as in the comparatively-high atmospheric pressure
environment. Also, the engine 11 is in a condition to be able to
supply a driving power corresponding to a hydraulic load caused by
an external force without experiencing a problem such as a decrease
in the engine revolution speed or an engine stop.
[0095] When the arm 5 is brought into contact with the ground at
the time t2, the hydraulic load increases according to an increase
in the excavation reaction force. Then, as the hydraulic load
corresponding to the absorbing horsepower of the main pump 14
increases, the load of the engine 11 also increases. In response,
the supercharger 11a of the engine 11 can quickly increase the
boost pressure to maintain the predetermined engine revolution
speed.
[0096] Thus, when the atmospheric pressure is relatively low, the
controller 30 voluntarily increases the absorbing horsepower of the
main pump 14 before a lever operation is performed to maintain the
boost pressure at a comparatively high level so that the boost
pressure can be increased without delay after the lever operation
is performed. This in turn makes it possible to prevent a problem
such as a decrease in the engine revolution speed or an engine stop
from occurring when a lever operation is performed.
[0097] Next, an absorbing-horsepower increasing process according
to another embodiment is described with reference to FIG. 7. FIG. 7
is a flowchart illustrating another exemplary absorbing-horsepower
increasing process. In the absorbing-horsepower increasing process
of the present embodiment, a determination condition used at step
S11 is different from the determination condition used at step S1
of the absorbing-horsepower increasing process of FIG. 5. However,
steps S12 through S14 are the same as steps S2 through S4 of the
absorbing-horsepower increasing process of FIG. 5. Accordingly,
step S11 is described in detail, and descriptions of other steps
are omitted here. Also in the present embodiment, the switcher 50
is omitted, and the controller 30 can always provide the functions
of the boost-pressure increase determiner 300 and the
absorbing-horsepower controller 301. However, instead of omitting
the switcher 50, the shovel may be configured such that the
switcher 50 is always turned on.
[0098] At step S11, the boost-pressure increase determiner 300
determines whether it is necessary to increase the boost pressure.
In the present embodiment, the boost-pressure increase determiner
300 determines whether the shovel is in the standby mode and the
atmospheric pressure around the shovel is less than a predetermined
pressure. In the present embodiment, the controller 30 determines
whether the atmospheric pressure around the shovel is less than the
predetermined pressure, i.e., whether the shovel is at high
altitude, based on an output from the atmospheric pressure sensor
P1 of the shovel.
[0099] When it is determined that the above condition is satisfied
(YES at step S11), the controller 30 performs steps S12 and S13 to
increase and fine-tune the absorbing horsepower of the main pump
14L.
[0100] On the other hand, when it is determined that the above
condition is not satisfied (NO at step S11), the controller 30
performs step S14 to stop increasing the absorbing horsepower of
the main pump 14L if the absorbing horsepower is being increased.
This is because when the atmospheric pressure is comparatively
high, it is not necessary to voluntarily increase the boost
pressure.
[0101] With the absorbing-horsepower increasing process of FIG. 7,
the controller 30 can achieve advantageous effects similar to those
achieved by the absorbing-horsepower increasing process of FIG.
5.
[0102] Also, in the present embodiment where the output of the
atmospheric pressure sensor P1 is used, a target boost pressure may
be determined according to a detected atmospheric pressure. In this
case, the controller 30 may gradually or continuously change the
target boost pressure according to the detected atmospheric
pressure. That is, the controller 30 may be configured to gradually
or continuously change the pilot pressure generated by the pressure
control valve 31, the moving distance of the flow control valve
174, and the discharge pressure of the main pump 14L to achieve a
target boost pressure. With this configuration, the controller 30
can gradually or continuously control the absorbing horsepower
increased during the standby mode and can further reduce
unnecessary energy consumption.
[0103] Also, the controller 30 may be configured to obtain the
altitude of the current location of the shovel based on an output
of a positioning device such as a global positioning system (GPS)
device and map information, and to determine a target boost
pressure based on the obtained altitude.
[0104] With the above-described configuration of the controller 30,
when the boost-pressure increase determiner 300 determines that it
is necessary to increase the boost pressure, the
absorbing-horsepower controller 301 can voluntarily increase the
absorbing horsepower of the main pump 14L by controlling the
pressure control valve 31 and thereby increasing the discharge
pressure of the main pump 14L. The increase in the absorbing
horsepower of the main pump 14L increases the rotational load, the
fuel injection amount, and the exhaust pressure of the engine 11,
increases the rotational speed of the turbine, and increases the
rotational speed of the centrifugal compressor in this order, and
eventually increases the boost pressure of the supercharger 11a.
Thus, the controller 30 can increase the boost pressure of the
supercharger 11a before the hydraulic load increases, and can
quickly increase the boost pressure along with the increase in the
hydraulic load without delay. Accordingly, the controller 30 can
improve the responsiveness of a hydraulic actuator and the
performance of the shovel at high altitude.
[0105] In the above embodiments, the operator turns on the switcher
50 to activate the absorbing-horsepower increasing function when
the shovel is at high altitude (in a comparatively-low atmospheric
pressure environment), or the shovel automatically activates the
absorbing-horsepower increasing function when the atmospheric
pressure is less than a predetermined pressure. Accordingly, the
controller 30 can voluntarily increase the absorbing horsepower of
the main pump 14 before a lever operation is performed and thereby
maintain the boost pressure at a comparatively high level so that
the boost pressure can be increased without delay after the lever
operation is performed. This in turn makes it possible to prevent a
problem such as a decrease in the engine revolution speed or an
engine stop from occurring when a lever operation is performed.
Also, the operator may turn on the switcher 50 to activate the
absorbing-horsepower increasing function even when the shovel is
not at high altitude. For example, the operator may turn on the
switcher 50 to activate the absorbing-horsepower increasing
function when generation of black smoke due to incomplete
combustion of fuel is detected. Also in this case, the controller
30 can voluntarily increase the absorbing horsepower before a lever
operation is performed and thereby maintain the boost pressure at a
comparatively high level so that the boost pressure can be
increased without delay after the lever operation is performed.
Thus, the controller 30 can suppress or prevent the generation of
black smoke.
[0106] Also in the above embodiment, the absorbing-horsepower
controller 301 increases the absorbing horsepower of the main pump
14 to increase the boost pressure when the boost-pressure increase
determiner 300 determines that the shovel is in the standby mode.
However, during the standby mode immediately after the operation of
a hydraulic actuator is stopped, the absorbing-horsepower
controller 301 may be configured to not increase the absorbing
horsepower of the main pump 14 until a predetermined time period
passes. More specifically, the absorbing-horsepower controller 301
may be configured to not output a current command to the pressure
control valve 31 until a predetermined time period passes after an
operation lever corresponding to an operated hydraulic actuator
returns to the neutral position. This is because the boost pressure
rises and falls slowly and is still at a high level until the
predetermined period passes. Also, the absorbing-horsepower
controller 301 may be configured to not output a current command to
the pressure control valve 31 until the output (boost pressure) of
the boost pressure sensor P3 becomes lower than a predetermined
value.
[0107] Also in the above embodiment, the absorbing-horsepower
increasing function is implemented by using an unused valve
position of a flow control value in the control valve system 17
which is already used for another purpose. Specifically, the
absorbing-horsepower increasing function is implemented by using
the left valve position (L) of the flow control valve 175
corresponding to the boom cylinder 7. However, the present
invention is not limited to this configuration. For example, the
absorbing-horsepower increasing function may be implemented by
using an unused flow control valve in the control valve system
17.
[0108] Also in the above embodiment, the absorbing-horsepower
controller 301 controls the pressure control valve 31 to move the
flow control valve 175 and increase the discharge pressure of the
main pump 14L, and thereby increases the absorbing horsepower of
the main pump 14L. However, the absorbing-horsepower controller 301
may be configured to move another flow control valve by controlling
the pressure control valve 31 in order to increase the discharge
pressure of the main pump 14R and thereby increase the absorbing
horsepower of the main pump 14R. Also, the absorbing-horsepower
controller 301 may be configured to move one or more flow control
valves by controlling the pressure control valve 31 to increase the
discharge pressures of the main pumps 14L and 14R and increase the
absorbing horsepower of the main pumps 14L and 14R at the same
time.
[0109] FIG. 8 is a drawing illustrating an exemplary configuration
of a hydraulic system that includes additional flow control valves.
Specifically, different from the hydraulic system of FIG. 3, the
hydraulic system of FIG. 8 includes a flow control valve 175 that
does not have the left valve position (L), a flow control valve
179, and relief valves 180L and 180R. Other components of the
hydraulic system of FIG. 8 are substantially the same as those of
the hydraulic system of FIG. 3. Accordingly, differences between
these hydraulic systems are described in detail, and descriptions
of the same components are omitted here.
[0110] In the present embodiment, the absorption-horsepower
controller 301 introduces the hydraulic oil into a pilot port of
the flow control valve 179 to move the flow control valve 179 from
the right valve position toward the left valve position. The flow
control valve 179 moved toward the left valve position limits the
flow rate of the hydraulic oil flowing through the center bypass
pipe line 40L and increases the discharge pressure of the main pump
14L.
[0111] Also in the present embodiment, the flow control valve 179
is disposed in the control valve system 17. Specifically, to be
able to quickly decrease the negative control pressure, the flow
control valve 179 is disposed at the most downstream position on
the center bypass pipe line 40L, i.e., at a position that is
downstream of the flow control valve 177 and upstream of the
negative control throttle 18L. Also, the flow control valve 179 may
be disposed in the control valve system 17 at a position that is
upstream of one of the flow control valves 171, 173, 175, and 177.
In other words, the flow control valve 179 may be disposed at a
position that is downstream of one of the flow control valves 171,
173, and 175 or at a position between the flow control valve 171
and the main pump 14L. As the position of the flow control valve
179 becomes closer to the main pump 14L, the flow control valve 179
can more quickly increase the discharge pressure of the main pump
14L.
[0112] The relief valves 180L and 180R are provided to maintain the
pressure of the hydraulic oil in the hydraulic system at a value
less than or equal to a predetermined relief pressure.
Specifically, the relief valves 180L and 180R open to discharge the
hydraulic oil into the hydraulic oil tank when the pressure of the
hydraulic oil in the hydraulic system becomes greater than or equal
to the predetermined relief pressure. For example, the relief valve
180L opens to discharge the hydraulic oil into the hydraulic oil
tank when the center bypass pipe line 40L is blocked by the flow
control valve 179 and the discharge pressure of the main pump 14L
becomes greater than or equal to the predetermined relief
pressure.
[0113] Also in the above embodiment, the absorbing-horsepower
controller 301 controls the pressure control valve 31 to move the
flow control valve 175 on the center bypass pipe line 40L and
increase the discharge pressure of the main pump 14L, and thereby
increases the absorbing horsepower of the main pump 14L. However,
the absorbing-horsepower controller 301 may be configured to move
another flow control valve on the center bypass pipe line 40L by
controlling the pressure control valve 31 in order to increase the
discharge pressure of the main pump 14R and increase the absorbing
horsepower of the main pump 14R.
[0114] Also in the above embodiment, the absorbing-horsepower
controller 301 controls the pressure control valve 31 to move the
flow control valve 175, which is a three-position spool valve, and
to increase the discharge pressure of the main pump 14L, and
thereby increases the absorbing horsepower of the main pump 14L.
However, the absorbing-horsepower controller 301 may be configured
to move another flow control valve, which is a four-position spool
valve, by controlling the pressure control valve 31 in order to
increase the discharge pressure of the main pump 14L and thereby
increase the absorbing horsepower of the main pump 14L. The
four-position spool valve is a flow control valve that is obtained,
for example, by adding one valve position for the
absorbing-horsepower increasing process to the flow control valve
171 that is a three-position spool valve.
[0115] Next, an absorbing-horsepower increasing process according
to another embodiment is described with reference to FIG. 9. FIG. 9
is a flowchart illustrating another exemplary absorbing-horsepower
increasing process. In the absorbing-horsepower increasing process
of this embodiment, the absorbing horsepower of the main pump 14 is
temporarily and voluntarily increased when a lever operation is
started regardless of the level of the atmospheric pressure. For
this reason, in the present embodiment, the switcher 50 is omitted,
and the controller 30 can always provide the functions of the
boost-pressure increase determiner 300 and the absorbing-horsepower
controller 301. However, instead of omitting the switcher 50, the
shovel may be configured such that the switcher 50 is always turned
on.
[0116] In the absorbing-horsepower increasing process of the
present embodiment, a determination condition used at step S21 is
different from the determination condition used at step S1 of the
absorbing-horsepower increasing process of FIG. 5. However, steps
S22 through S24 are the same as steps S2 through S4 of the
absorbing-horsepower increasing process of FIG. 5. Accordingly,
step S21 is described in detail, and descriptions of other steps
are omitted here.
[0117] At step S21, the boost-pressure increase determiner 300
determines whether it is necessary to increase the boost pressure.
In the present embodiment, the boost-pressure increase determiner
300 determines whether the shovel is in the standby mode and a
lever operation is started. Also in the present embodiment, the
controller 30 determines whether a lever operation is started based
on an output from the pressure sensor 29.
[0118] When it is determined that the above condition is satisfied
(YES at step S21), the controller 30 performs steps S22 and S23 to
increase and fine-tune the absorbing horsepower of the main pump
14L.
[0119] On the other hand, when it is determined that the above
condition is not satisfied (NO at step S21), the controller 30
performs step S24 to stop increasing the absorbing horsepower of
the main pump 14L if the absorbing horsepower is being increased.
This is because when no lever operation is started, it is not
necessary to voluntarily increase the boost pressure.
[0120] Thus, the controller 30 temporarily and voluntarily
increases the absorbing horsepower of the main pump 14 when a lever
operation is started. That is, the controller 30 increases the
engine load before the load of a hydraulic actuator increases. With
this configuration, the controller 30 can apply a predetermined
load to the engine 11 and increase the boost pressure of the
supercharger 11a even when no hydraulic load is being applied by an
external force. In other words, the controller 30 can increase the
boost pressure by a predetermined amount before the hydraulic load
increases due to an external force without directly controlling the
engine 11 and the supercharger 11a. As a result, even in a case
where the hydraulic load rapidly increases due to an external
force, the supercharger 11a can generate a boost pressure
corresponding to the increasing hydraulic load before a problem
such as a decrease in the engine revolution speed (a decrease in
performance) or an engine stop occurs. When the increase in the
boost pressure does not keep up with an increase in the hydraulic
load (engine load) resulting from an external force, the engine 11
cannot sufficiently increase the fuel injection amount. As a
result, the engine revolution speed decreases and in some cases,
the engine 11 may stop without being able to increase the engine
revolution speed.
[0121] Next, temporal changes in physical quantities, which are
observed when the absorbing-horsepower increasing process of FIG. 9
is performed, are described with reference to FIG. 10. FIG. 10 is a
drawing illustrating temporal changes in physical quantities
including the lever operation amount, the hydraulic load (the
absorbing horsepower of the main pump 14), the boost pressure, the
fuel injection amount, and the engine revolution speed arranged in
this order from the top. In FIG. 10, each solid line indicates a
temporal change when the absorbing-horsepower increasing process of
FIG. 9 is performed, and each dashed line indicates a temporal
change when the absorbing-horsepower increasing process of FIG. 9
is not performed.
[0122] In FIG. 10, it is assumed that a lever operation is started
at a time t1 to move, for example, the arm 5 for excavation.
[0123] First, for comparison, temporal changes in physical
quantities observed when the absorbing-horsepower increasing
process of FIG. 9 is not performed are described. The temporal
change of the lever operation amount of the arm operation lever is
the same as that in FIG. 6, and therefore its description is
omitted here.
[0124] When the absorbing-horsepower increasing process of FIG. 9
is not performed, the hydraulic load (dashed line) does not
increase until the time t2. Then, when the arm 5 is brought into
contact with the ground at the time t2, the hydraulic load
increases according to an increase in the excavation reaction
force.
[0125] Also, the boost pressure (dashed line) does not increase
until the time t2 and is at a comparatively low level even at the
time t2. Therefore, the supercharger lie cannot increase the boost
pressure along with the increase in the hydraulic load after the
time t2. As a result, the engine 11 cannot sufficiently increase
the fuel injection amount, cannot output sufficient engine power,
cannot maintain the engine revolution speed (the dashed line), and
may stop without being able to increase the engine revolution
speed.
[0126] On the other hand, when the absorbing-horsepower increasing
process of FIG. 9 is performed, the hydraulic load (solid line)
starts to increase at the time t1 and reaches a predetermined level
before the time t2. In this case, when the start of operation of
the arm operation lever is detected at the time t1, the controller
30 controls the pressure control valve 31 to increase the discharge
pressure of the main pump 14 for a predetermined time period before
a load is applied to the corresponding hydraulic actuator. Here,
the predetermined time period is a very short period (e.g., about
0.3 sec) that is sufficiently shorter that the time period between
the time t1 and the time t2. Also, the controller 30 may increase
the discharge rate of the main pump 14 in addition to the discharge
pressure by adjusting the regulator 13. This configuration makes it
possible to increase the absorbing horsepower of the main pump 14
before the discharge pressure of the main pump 14 increases due to
a load applied to the arm 5. Then, as the hydraulic load
corresponding to the absorbing horsepower of the main pump 14
increases, the load of the engine 11 also increases. In response,
the supercharger lie of the engine 11 increases the boost pressure
to maintain the predetermined engine revolution speed. As a result,
the boost pressure (solid line) starts to increase at the time t1
and reaches a predetermined level before the time t2. Therefore,
even after the time t2, the supercharger 11a can increase the boost
pressure along with the increase in the hydraulic load without much
delay. Accordingly, the engine 11 can output sufficient engine
power and maintain the engine revolution speed. Specifically,
except for a slight decrease caused by the voluntary increase of
the hydraulic load during a period between the time t1 and the time
t2, the engine revolution speed (solid line) is maintained at a
constant level.
[0127] Thus, the controller 30 voluntarily increases the hydraulic
load not resulting from an external force after a lever operation
is started and before the hydraulic load increases due to an
external force such as an excavation reaction force. Then, the
controller 30 increases the absorbing horsepower of the main pump
14 to increase the engine load and thereby indirectly causes the
supercharger 11a of the engine 11 to increase the boost pressure to
a comparatively high level. Accordingly, even when the hydraulic
load rapidly increases due to an external force such as an
excavation reaction force, the controller 30 can quickly increase
the boost pressure that is already at a comparatively high level.
This in turn prevents a problem such as a decrease in the engine
revolution speed (a decrease in performance) or an engine stop from
occurring when the boost pressure is increased.
[0128] The absorbing horsepower increasing process described with
reference to FIGS. 9 and 10 may be performed by either one of the
hydraulic system of FIG. 3 and the hydraulic system of FIG. 8.
[0129] A shovel and a method of controlling the shovel according to
embodiments of the present invention are described above. However,
the present invention is not limited to the specifically disclosed
embodiments, and variations and modifications may be made without
departing from the scope of the present invention.
[0130] For example, although a hydraulically-driven rotating
mechanism 2 is used in the above embodiment, an electrically-driven
rotating mechanism 2 may instead be used.
[0131] Also, although an application of the present invention to a
hydraulic shovel is described in the above embodiments, the present
invention may also be applied to a hybrid shovel where the main
pump 14 is driven by the engine 11 and a motor generator connected
to the main pump 14. Further, the present invention may be applied
to any construction machine such as a crane, a lifting magnet
crane, or an asphalt finisher that includes a supercharger, an
internal combustion engine controlled at a constant revolution
speed, and a hydraulic pump.
* * * * *